Wall Shear Wood Tension Capacity

Function

• Lateral loads such as seismic activity and high force winds create tension on a building's roof structure. The lateral loads are transferred from the rooftop to horizontal diaphragms, which can be roofs, floors or other horizontal bracing structures. These loads are then shifted to shear walls in the building. Shear walls, whether made of wood or masonry, transfer these loads to the foundation of the building. This process increases the building's tensile strength or overall capacity to resist tension from loading.

Shear Wall Design

• Generally, shear walls are divided into two design types: segmented design and perforated design. Wood shear walls are divided into sections exhibiting a combination of wall openings and full height sheathing. Wall openings are usually windows and doors. Perforated shear walls are similar to segmented designs. However, wood shear walls using a perforated shear wall design install hold-down connectors at either end of the wall. In contrast, segmented shear walls install hold-down connectors at the bottom corners of each wall segment to minimize overturning.

Wood Species

• As sheathed components in buildings, shear walls consist of long panels of wood that comprise lumber, plywood or wood lath. The density of these materials affects fastener strength and its ability to hold onto the wood. For example, douglas-fir is one wood species that has high density and provides a strong and secure surface for fasteners. In comparison, redwood and hem-for shear walls possess low density and are weaker than douglas-fir structures, according to the Association of Bay Area Governments.

Advantages

• One of the advantages of using wood in shear wall design is the lumber’s capacity to absorb impact loads, according to the Engineered Wood Association. Wood shear walls will continue carrying building loads, while supporting a significant amount of tension and stress. Moreover, the Canadian Sheet Steel Building Institute recommends using plaster in combination with wood panels to increase shear capacity in buildings with height limitations. The presence of wood increases the shear wall’s ability to effectively transfer loads and resist tension caused by ground movement and other lateral forces.